Direct current motors and generators are used in many applications, including train locomotives. Such machines have a stator and a rotor in a housing. The rotor has several coils and a cylindrical commutator, and the commutator has a plurality of electrical contacts separated by insulators. Electric current is supplied to the rotor coils through the commutator contacts and electrically conductive brushes secured to the machine housing. The brushes are pressed against the commutator contacts by springs.
With use, the brushes wear down the outer surface of the commutator, often unevenly. If the surface is excessively uneven, with significant irregularities, the brushes will momentarily lose contact with the commutator surface as the commutator rotates, causing arcing and possibly significant damage to the machine.
To avoid such arcing, the outer surface of the commutator must be periodically measured for roundness and smoothness by removing the rotor and placing it in a lathe or the like. A linear voltage differential transducer, or LVDT, is placed against a selected portion of the commutator, and a reference output voltage is set. The commutator is then rotated, and changes in the radius of the commutator, including those which occur where there are irregularities in the outer surface of the commutator, are electronically measured and recorded on a chart recorder. The recorded output signals of the LVDT are analyzed to determine whether or not the commutator must be repaired. This system is inefficient if repairs are not needed, however, because a great deal of time is required to remove the rotor, install it in a lathe, and replace the rotor in the machine. It is particularly inefficient with locomotives and other applications where the machines are large and heavy. Thus, there is a need for methods and a system for measuring the roundness of the outer surface of a commutator to identify irregularities, without removing the rotor from the machine.
Accordingly, one object of this invention is to provide new and improved methods and a system for identifying and measuring irregularities in the outer surface of a commutator.
Another object is to provide new and improved methods and a system for identifying and measuring irregularities in a commutator surface, without removing the commutator from the machine in which the commutator is installed.